Abstract
Winter synoptic conditions that produce snowfall with bitterly cold temperatures create both social and economic hazards in the capital city of Albany, NY. Sometimes these systems are forecasted in error to produce rain or mixed precipitation. It is beneficial for meteorologists to better understand the commonly used 5400 and 1300 GPM line to better forecast rain versus snow events. Other studies have looked into the use of the 5400 GPM (540 dm) line but none have assessed the validity of this boundary with respect to weather type characterization at Albany. This study aims to determine the reliability of the widely referenced guides for depicting the rain-snow line, and improve forecast aids for the vertical atmosphere during winter precipitation events. The mean daily 500, 850, 925 and 1000 mb heights and weather type frequency of the Spatial Synoptic Classification between November and March of 1980 - 2012 are analyzed. Results indicate that the standard vertical boundaries are inaccurate indicators of a rain versus snow event in Albany. More reasonable rain-snow cut offs for the 1000 - 500 and 1000 - 850 mb thicknesses are 5222 and 1262 GPM. For the 1000 - 925 mb level, 606 GPM is a helpful aid of identifying the rain-snow boundary. Further scrutinizing by weather type indicates that the rain-snow boundary also varies depending on what air mass/weather type is present on a given day. For instance, when the most prominent weather type is observed over Albany (Dry Polar), at the 1000 - 850 mb and 1000 - 500 mb layers, a boundary of 1242 GPM and 5152 GPM is found to be most representative. Results indicate only for the rarest of winter weather types observed over Albany, Moist Tropical, are the standard cut offs useful. Determining the reliability of this precipitation indicator at a specific station, like Albany, could enable meteorologists in other regions of the country to draw parallels between weather type, precipitation, and thickness in their forecast zones.
Highlights
In the Northeast, major winter storms that produce large snow totals cost cities like Albany, NY a great deal
This study aims to determine the reliability of the widely referenced guides for depicting the rain-snow line, and improve forecast aids for the vertical atmosphere during winter precipitation events
Further scrutinizing by weather type indicates that the rain-snow boundary varies depending on what air mass/weather type is present on a given day
Summary
In the Northeast, major winter storms that produce large snow totals cost cities like Albany, NY a great deal. The 2018 annual snow contract highlights the cost of handling these events, as the city was approved for the amount of $1,403,721 for snow removal [4]. Accurate prediction of these storms is a difficult task, but perhaps a greater challenge for Albany forecasters comes with deciphering between events that produce snow and those with rain, and/or mixed precipitation. Two prominent examples are when residents expect the first predicted snowstorm of the year to come and nothing manifests and when a strongly hyped mid-winter snowfall event is predicted but weakens before reaching the city, producing some mixed precipitation and rain rather than snow
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